Method for preventing corrosion of ferrous metals



United States Patent IVIETHOD FOR PREVENTING CORROSION OF FERROUS METALS Charles Bryce Hutchison, Webster Groves, Mo., assignor to Petrolite Corporation, Wilmington, Del., acorporation of Delaware No Drawing. Filed Nov. 30, 1956, Ser. No. 625,249

8 Claims. (Cl.- 252-855) This invention relates to the prevention of corrosion and more particularly to the inhibition 'of corrosion of ferrous metals.

The corrosion inhibiting aspect of this inventionmay be illustrated by a method for inhibiting corrosion of ferrous metals by hydrocarbon fluids containing water and a member of the group of corrosive materials consisting of hydrogen sulfide, carbon dioxide, organic acids containing 2 to 4 carbon atoms per molecule, combinations of these materials with: each other, combinations of each of said corrosive materials withoxygen, and combina- I tions of said materials with each other and oxygen, comprising adding to said fluids at least 5" parts per million of the soluble basic reaction. product obtained by heating below the pyrolytic point a diamide' of: the formula in which RCO is the naphthenyl radical of a naphthenic acid within the molecular weight range of 200 to- 500; R is an alkylene radical having not over 6 carbon atoms, R is a member of the class selected from hydrogen and low molal alkyl radicals having less than 8 carbon atoms, and n is a small whole number varying from 1 to 4; said diamide derived product involving at least one of two reactions of the class consisting of polymerization a'ndd'ehydration; said product being. further characterized bythe absence of a cyclic amidine structure and said dehydration of the diamide eliminating from .5 to 1.5 moles of water per molecule of diamide.

More specifically, this phase of the invention relates to the inhibition of corrosion in the petroleum industry with specific reference to producing wells, pipe lines, refineries, tank storage, etc.

The use of a corrosion inhibiting agent in the oil industry and other industries, and particularly for the protection of ferrous metals, is well known. For example, see U.S. Patents No. 2,736,658, dated February 28, 1956, to Pfohl et al., and 2,756,211, dated July 24, 1956, to Jones. and 2,727,003 dated December 13, 1955, to Hughes.

More specifically then, and particularly from the standpoint of oil production, this aspect of the invention relates to inhibiting corrosion caused by hydrogen sulfide, carbon dioxide, low-molecular-eombinations of each with oxygen or with each other and oxygen. More particularly, it relates to treating' wells to mitigate metal corrosion and associated difficulties.

As to the employment of corrosion inhibiting agents in the petroleum industry one need only refer to excerpts from the above patents as clearly indicating the field of application. For instance, the following excerpt from U.S. Patent 2,736,658 applies in the instant situation:

It is a general object of this invention to provide a novel method for protecting metal surfaces from'corrosion involving the use of a class of corrosion inhibitors Est:

whose unexpectedly superior corrosion inhibiting properties were discovered in the course of the experimental work leading to the present invention. More specifiwlly, it is-an object of this invention to provide a method and a means for protecting ferrous metal surfaces against corrosion by the action of oxygen and water. In this connection, it is an object of this invention to provide a corrosion inhibiting method which is capable of protecting' ferrous metal surfaces which are normally in contact with atmospheric air, and also ferrous metal surfaces which are normally or at least periodically in contact with liquids containing dissolved water, oxygen and other corrosion compounds or elements. It is a still further object of this invention to provide corrosion inhibitor compositions for use in the method of this invention, and particularly corrosion inhibitor compositions in which the liquid or solid carrier for the corrosion inhibitor co operates with the inhibitor to increase its effectiveness in protecting metal surfaces, and particularly ferrous metal surfaces. Again, reference is made to an excerpt from aforementioned U.S. Patent 2,727,003 which also applies with equal force and effect in regard to the instant invention:

It should' also be-p'ointed out that the corrosiveness of oil well brine's willvary' from well to well, and the proportion of. corrosion inhibiting agent added to the well fluids should also be varied from well to well. Thus, in some wells it may be possible to effectively control corrosion by the additionof as'little as I0 ppm. of my new compositions to the well fluids, Whereas in other wells, it may be necessary to add 200- p.p.m. or more.

In using my improved compositions for protecting oil well tubing; casing, and other equipment which comes in contact with the corrosive oil-brine production, I find that excellent results may be obtained by injecting an appropriate quantity of a selected composition into a producing well-so that it may mingle with the oil-brine mixture and come into contact with the casing, tubing, pumps and other producing equipment. I may, for example, introduce the inhibiting composition into the top of the casing, thus causing it to flow down into the well and thence back through the tubing, etc. In general, I have found that this procedure suffices to inhibit corrosion throughout the entire system of production, and collection, even including field tankage.

As a matter of fact, What is said above is in essence the equivalent of what appears in U.S. Patent Re. 23,227, dated May 9', 1950, to Blair et al., at columns 9, 10 and 11.

Specific reference is made to aforementioned U.S. Patent 2,756,211. Indeed, with a slight change in text the following is essentially a verbatim excerpt of a paragraph in said patent:

In case series emulsion or gel problems are encountered, demulsifiers may be added. This is important not only to avoid the troublesome emulsions and gels themselves, but also to improve corrosion inhibition. The explanation of less effective corrosion inhibition in the presence of emulsions apparently is that the inhibitor is somewhat surface-active. That is, it is concentrated at interfacial surfaces. Since this surface is great in an emulsion, most of the inhibitor will be concentrated in these interfaces and little will remain in the body of the oil for deposition on the metal surfaces. In many wells, oil-in-water type emulsions often occur naturally. In such wells the inhibitors herein described tending to form water-in-oil type emulsions, often decrease the emulsion problems naturally present. Thus, in addition to being effective corrosion inhibitors, the herein described products tend to eliminate emulsion problems which sometimes appear when some of the present day inhibitors are used in oil wells or refinery processing.

For convenience, what is said hereinafter will be divided into six parts:

Part 1 is concerned with the composition or structure of the non-cyclic dehydration and/or polymerization products obtained by the elimination of one mole of water, or approximately so, from a diamide;

Part 2 is concerned with polyamines of the kind suitable for reactants in the preparation of the herein described corrosion inhibiting agent;

Part 3 is concerned with naphthenic acids;

Part 4 is concerend with the preparation of the herein described corrosion inhibitors and for purpose of convenience will be divided into two sections; Part 4, Section A, is concerned with the preparation of diamides; Part 4, Section B, is concerned with the preparation of dehydration and/or polymerization products by elimination of one mole of water or a substantial fraction thereof from the diamide. Needless to say, the herein described dehydration and/or polymerization product is obtained on a practical scale in a single step operation. One need not stop at the diamide stage and then convert. However, the products are best characterized by noting the structure of the diamide and thus for purpose of convenience such presentation is herein employed.

Part 5 is concerned with mixing the corrosion inhibiting agent with suitable solvents or converting it into salts in which oil solubility or at times water solubility is increased, so as to yield a product most suitable for use in oil field or refinery practice by means of a metering pump, and also moreuseful in other industrial applications;

Part 6 .is concerned with specific examples of the utility and effectiveness of the herein described corrosion inhibitors.

' PART 1 The formation of diamides from a monocarboxy acid and apolyamine is well known. The conversion of a monoamide or a diamide, as the case may be, into cyclic amidine, such as an imidazoline, is well known. For instance, in the case of stearic acid and tetraethylene pentamine it may be illustrated thus:

((IJIHINEDBH Z-heptadeeyl l-tri- (aminoethylene) imidazoline However, if one examines the structural formulas of a typical naphthenic acid of the kind herein employed and described in Part 3 following, it is obvious that steric hindrance would be expected to prevent the formation of the cyclic amidines. See, for example, J.A.C.S., vol. 61, November 19, 1939, pp. 3195-7. The author is Aspinall. Such specific explanation in respect to such reaction, or similar reaction, appears in US. Patent No. 2,291,396, dated July 28, 1942, to Lieber, as follows:

Although the mechanism of the operation of this invention is not well understood, it is believed that the following reactions occur:

l Heat (-1110) Stearic acid Tetraethylene pentamine lHeat (-HgO) Also, intro-molecular nitrile formation is possible. There is also a possibility that upon heating, the OH group of the fatty acid may combine with a hydrogen in the amine compound, for instance, with the hydrogen in the NH group, with the resultant liberation of water vapor and the consequent formation of an acyl derivative of the polyalkylene polyamine and subsequent polymerization.

The above reaction of course is a conventional one and in essence depends on the migration of the hydrogen atom attached to nitrogen to the oxygen atom double bonded to carbon, thus .forming a single bonded hydrogen atom and the double bond between the carbon and nitrogen atoms. 1

However, in the preparation of products following the use of naphthenic acids even with a triamine the final product invariably is basic indicating the presence of at least one basic nitrogen radical. Further attention is directed-to the infrared spectrogram of a product of the kind described in Part 4 and derived from the reaction of one mole of diethylene triamine and 2 moles of naphthenic acid with elimination of 3 moles of water. Examination of the infrared spectrogram clearly indicates the absence ofa cyclic amidine (imidazoline) radical and thus is in agreement with the Aspinall reference as above noted. For this reason the herein specified products have been characterized as the basic derivatives obtained from polyamines of the kind described in Part 2 in combination with the acids described in Part 3 with the proviso that the initial reactant ratio be two parts of acid to one of'amine withthe elimination of any excess, with .two moles of water-and not over 3.5. moles of .water per moleof amine-without ring'formation.

PART 2 The polyamines employed are alkylene polyamines having at least 3 basic nitrogen atoms and characterized by the fact that they are terminally acylation susceptible so as to yield diamides, i.e., susceptible to acylation in each terminal position. They correspond to the following formula:

I H I R1 N R [R] N u They may consist, however, of a hexamethylene radical, i.e., as many as 6 carbon atoms.

As is well known, low molal amines, such as methylamine, ethylamine, or cyclohexylamine, can be treated with either 2 moles of ethylene imine or two moles of acrylonitrile followed by reduction to yield amines of the type in which R is a low molal alkyl group and R and R,

are hydrogen. The two occurrences of R need not be identical as, for example, similar reactants involving ethylene diamine and propylene imine, or ethylene diamine and one or two moles of acrylonitrile, followed by reductlon.

vpentamine and mixtures of higher. amines such as hexamines, heptamines, etc.

Another suitable amine, although higher in price than those above noted, is 3,3'--iminobispropylamine.

PART 3 The monocarboxy acids employed in the present invention as reactants are naphthenic acidsi As to the description of naphthenic acids reference made .to Industrial ,& Engineering Chemistry, vol. 41, No. 1 0, sOctober 1949, pages 2080-2090, as follows:

The most widely used is naphthenic acid, a petroleum refining by-product obtained when the alkali liquor from the caustic treatment of gas oil is acidified with-sulfuric acid. This treatment produces a dark brown about 12 on the Gardner color scale when cut 1 to 9 with mineral spirits) oily liquid which separates to the top of the aqueous liquor. The mixed acids can be divided roughly into three groups having the general formulas: C H O C H and C H O The first group occurs largely in the lower boiling fraction of the mixture. They usually contain 6 or 7 carbon atoms and are colorless. The second group, usually the largest, contains acids of 8 to 12 carbon atomshaving the structure:

HzC CH:

The third group contains the. heaviest molecules which are polycyclic and have from 12 to 23 carbon atoms. All fractions from a carefully distilled naphthenic acid (24) contain some color which, so far, has proved impossible to remove. Tarry residues account for the dark color of the crude, but these are largely removed by distillation. Since naphthenic acids are saturated and primarily cyclic, their soaps havevmuch greater stability than those of other common liquid acids. The crude acid as delivered has a density of 8.04 to 8.44 pounds per gallon and a viscosity of 1.25 poises at 77 F. The acid values range from 160 to 270, but naphthenic acid used for soap manufacture usually has an acid value between 220 and 230. pH of the water extract is about 5.5 and the iodine value between 8 and 11. Unsaponifiables are held below 12%. The initial boiling points vary widely from shipment to shipment. Individual batches have boiled below 200 F. and up to almost 400 F. at 3.5 inches of mercury.

A typical formula in connection with some of the commercially available naphthenic acids is the following:

H H H C CH: CH: OH: H O my all-..

H l l l --CH1 wax l t 6 used but preference is to use the commercial grades above described, or in some instances, mixtures of two dilferent grades so as to give, for example, an average molecular weight of 360 to 370 in some instance, and in others, a molecular weight of about 310, or thereabouts.

In examining the formula immediately preceding, with the formula preceding the above formula, and ignoring difierence in the cyclic structure of the naphthenic acids, it is apparent that in at least some naphthenic acids which are available commercially the cyclic structure is part of the beta carbon atom. On the other hand, as far as is known, and referring to the formula HLC CB1:

(CH1) 1C0 OH there are available naphthenic acids in which apparently x in the formula represents a small whole number, for instance, 3 or 4 or the like. There is no reason to believe such naphthenic acids cannot be converted into cyclic ami dines.

The present invention is limited to naphthenic acids commercially available which do not form cyclic amidines. The claims specify that the product be free from a cyclic amidine structure, i.e., from an imidazoline structure, or a tetrahydropyrimidine structure. There is ,no difficulty in verifying the nature of thefinished product in this respect. All that is necessary is appropriate infrared spectrogram whichs'hows the absence of a cyclic amidine structure.

,PART4 SectionA As has been pointed ,out previously, the manufacture "of diarnides from one mole of a polyamine of the kind herein employed as a reactant and 2 moles of naphthenic acid, is a procedure that is well known and simply means heating under such conditions as will convert the salt form into an amide by the elimination of 2 moles of water per mole of polyarnine. The reaction sometimes is conducted by merely heating, other times by heating in vacuum, and other times using an insoluble solvent such as xylene to eliminate water formed. However, for the majority of purposes there is no need for a twostep process and thus Part 4, Section B, following includes data which in part is pertinent to the manufacture of a 'diamide.

Section B The naphthenic acids herein employed for the purpose of convenience may be indicated thus: RCOOH in which RC0 is the naphthenyl radical. In light of what has been said previously it is obvious that by reacting one mole of a suitable polyamine with 2 moles of a suitable naphthenic acid one could readily obtain a in which 'R"CO is the naphthenyl radical of a naphthenic acid within the molecular weight range of 200 to 500; R is an alkylene radical having not over 6 carbon atoms; R is a member of the class selected from hydrogen and low molal alkyl radicals having less than 8 carbon atoms, and n is a small whole number varying from 1 to 4; said diamide derived product involving at least one of two reactions of the class consisting of polymerization and dehydration; said product being further characterized by the absence of a cyclic amidine structure and said dehydration of the diamide eliminating from .5 to 1.5 moles of water per molecule of di'amide.

In 'light of re-examination of the data, it seems it is quite likely the effective agent may be a nitrileam'ide, i.e., one terminal being an amide group, the other one anitrile group, thus:

It has been pointed out previously there seems tobe no question as to the composition of the diamide intermediate but there is a question as to the structure of the f dehydration and/or polymerization product obtained by the elimination of one mole of water, or approximately one mole of water, from the diamide. This has been discussed in Part 1, preceding.

In preparing the herein described compounds in a single step operation, it is preferred to mix the 2 moles of naphthenic acid and 1 mole of diethylene triamine and add benzene or xylene in order to make the mixture more fluid, and also to form azeotropes to carry ov erhead the water formed in the reaction.- The is then heated until water ceases to evolve 'overheadlitli e entrainer being continuously returned to the'i'eaction vessel. When the reaction temperature reaches an equilibrium so that the temperature can no longer be raised because all the heat is being used .to,vaporize the en- I trainer, the entrainer, such as benzene or1xylene,.i s removed as it distills off. The reaction may then be heated to about 280 C. for about 2 hours in order to be sure that the reaction has been driven to compltion, although this maintained heating is not absolutely necessary.

As pointed out for purpose of describing the invention reference is made to a two-step process which can be a single-step process as above noted. Under certain conditions, however, there is an advantage to a two-step process. For example, mixing two different diamides and then subjecting the mixture to the dehydration (or polymerization) step. It is doubtful that any specific example is required in any detail but purely by way of explanation the following is included: (Examples 1 to 4 appear in tabular form in Tables 1 and 2 along with tabulation of Example 5 and other examples.)

Example 5 at this temperature for about 2 hours to insure thatthe reaction had been driven to completion, although this maintained heating is not absolutely necessary. The resulting product was a dark brown resin of such high viscosity that it did not fiow readily at room temperature. The product was soluble in isopropyl alcohol, and the full range of hydrocarbons, including crude oil, kerosene and isooctane.

Note Example 5 is described again in tabular form with all thepertinent data in Tables 1 and 2, following.

Note also that Tables 1 and 2 illustrate a large number of examples of the present invention.

TAELE 1.DEHYDR.ATION AND/OR PoLYMERIzATroir rnonno'rs DERIVED BY ELIMINATION or ONE MOLE OF WATER, on A SUBSTANTIAL FRACTION THEREOF,

FROM A DIAMIDE OF THE FOLLOWING FORMULA:

N-R-[NR1-N R"C on" -Naphthenylradical Ex.'No. fromacidhavlngmol. R R, 'n wt.ot'approximately 323 C2114 H 1 323 CIHL H 2- '323 61H H 3 352 01114 H 1 352 CsHl H 1 352 CzH4 H 3 450 j 01H H 1 450 02H; H 2 450 01H CH: 3 323 C2114 CH3 2 352 02H OH: 2 450 CzH4 CH3 2 323 CaHa H 1 352 caHo H 1 450 Call: H l 352 CaHs CH3 1 323 I C2114 CizHzs 1 352 02114 H25 1 Mixtures, Parts 323 01114 H :32 g3 1 Part N==2 352 our H g zg ar =2 I 9 F i ar 7 ar 352 H {3 Parts N=1 Mixtures Parts I Part M.W. 323 ll thll- I ar g g fi vykgg 01m H 2 ar 25 {1 Part M.'W.450 H TABLE 2.-DEHYDRATION' ANDIOR- POLYMERIZATION PRODUCTS DERIVED BY ELIMINATION OF ONE to 1%) MIOLE OF WATER, OR A SUBSTANTIAL FRACTION THEREOF, FROM TWO DIAMIDES OF THE FOLLOWING FORMULA:

Ex. No.

Examination of the tabular data reveals that in some instances as little as one-half mole of water is eliminated per diamide dehydration; in other instances, as much as 1 /2 moles per mole of diamide dehydration. Reducing this ratio to a whole number, it means that in some instances dehydration eliminates one mole of water from 2 moles of diamide, and in some instances eliminates as much as 3 moles of water from 2 moles of diamide. .Reexamination of the previous formula concerned with polymerization by inter-molecular nitrile formation indicates the initial reaction might eliminate, and probably does eliminate, one mole of water from two moles and the diamide. Further reactions have taken place, particularly in derivatives, where there is more than one secondary amino radical, tetraethylene pentamine, for example, with the elimination of three moles of water from 2 moles of diamide.

The present invention is concerned with the use of materials in which a high molal group, i.e., 8 carbon atoms or more, is introduced by virtue of the naphthenyl radical. Although the preference is to use, for reasons of economy, the non-substituted amines such as diethylenetriamine, triethylenetetramine, tetraethylenepentamine, etc. The

mono-substituted polyamines may be employed such as the monomethylated, monoethylated, or monobutylated products, etc., provided the alkyl radical so introduced has less than 8 carbon atoms. This conforms to the requirement that the polyamino reactant have present at least 3 basic nitrogen atoms and a primary amino group and a secondary amino group.

There are available polyamines in which the terminal alkyl substituent has 8 carbon atoms or more, with particular reference to radicals Obtained from fatty acids having 12, 14, 16, 18 or more carbon atoms. It has been found these products also can be used in the manner herein described and in some instances give considerably greater oil solubility and have some inherent advantages. Furthermore, they have the peculiar advantage that products can be made in which certain low molal acids which do not form cyclic amidines can be employed. Such variants are not included in the present invention.

Reference is made elsewhere to the fact that the herein described corrosion inhibitors can be used in combination with other well known corrosion inhibitors. Reference is made to the cyclic amidine structures, the amido cyclic amidine structures, and the amino cyclic amidine structures, as disclosed in aforementioned Blair and Gross Reissue Patent No. 23,227. When the herein described products are mixed with corrosion inhibitors of the conventional type in the ratio of one-to-three, one-to-one, threeto-one, or the like, in numerous instances the effectiveness of the corrosion inhibitor thus obtained is significantly greater than the use of either one alone. The reason is not understood but this particular combination is not included as part of the present invention.

Reference to the basic products herein described and particularly for use as corrosion inhibitors includes not only the products as such but also in salt form and particularly combinations which tend to increase the solubility in a selected solvent or system as, for example, the addition of fatty acids, dimeric acids, naphthenic acids, or the like, to promote oil solubility; or the addition of acetic acid, hydroxyacetic acid, and the like, to promote solubility in a polar solvent such as water.

PART

Since these products are basic they can be combined wlth various acids to produce salts in which oil solubility is increased or decreased. Likewise, water solubility may vbe increased or decreased. For instance, the products What has been said in regard to the acids which increase oil solubility and decrease water solubility applies with equal force and effect to acids of the type, such as acetic acid, hydroxyacetic acid, gluconic acid, etc., all of which obviously introduce hydrophile character when they form salts or complexes, if complexes are formed.

As pointed out previously, the addition of corrosion inhibitors, particularly in the form of a solution by means of a metering pump or the like, is common practice. The particular corrosion inhibitors herein described are applied in the same manner as other corrosion inhibitors intended for use for the same purpose. For sake of brevity, as to the use of the corrosion inhibitor and its solution in a suitable solvent such as mineral oil, methyl ethyl ketone, xylene, kerosene, high boiling aromatic solvent, or even water, reference made to aforementioned Blair et al. patent, and particularly to columns 9 and 10, beginning with line 40 in column 9, through line 70 in column 10.

PART 6 The effectiveness of the compositions in inhibiting the corrosiveness of oil field brines may be better and more fully understood by reference to certain tests which have been conducted using synthetic oil field brines and a hydrocarbon that is essentially kerosene. The compositions were evaluated by test procedure outlined in the publication of the National Association of fCorrosion Engineers Corrosion, volume 2, No. 1, Correlation of the Results Obtained With Corrosion Inhibitors in the Laboratory and in the Field, by G. E. Purdy and William J. Ries.

Results of a typical test run are set forth in the following table, at inhibitor concentrations of 30 ppm.

Percent Inhibitor M01. Ratio Protection Nnnc 0 Commercial Inhibitor A 75 Commercial Inhibitor B 89 Commercial Inhibitor C 83 Commercial Inhibitor D- 76 Commercial Inhibitor E 75 89 lo 92 DET-i :aphtl1enic Acid:

Apparent M.W. 352 (330). 93 Apparent M.W. 450 (415). DPT-Naphthenic Acid, Apparent M.W. 352

(330) 1:2 93 TEP-N aphthenic Acid, Apparent M.W. 323

297 1:2 91 DET, TET-Naphthenic Acid, Apparent M.W.

In the above tabular data, DET is an abbreviation for diethylene triamine, TET is an abbreviation for triethylene tetramine, DPT is an abbreviation for dipropylene triamine. in the last example a 50%. mixture of a diamine and a triamine were employed.

Previous reference is made to the fact that commercial naphthenic acids frequently contain 6% to 10% of inert materials which cannot be economically separated. It is not unusual to ignore this fact in chemical molecular weight designation. Sometimes such molecular weights are referred to as apparent molecular weight. In the above table note the naphthenic acid employed has been expressed by both designations, i.e., the apparent moiecular weight frequently used in commerce and the true or equivalent molecular Weight indicated by the figures in parentheses.

In the above tests under the conditions noted which are typical of many oil field conditions, six well known or widely used competing products gave protection vary- .example, from about 85% to 92.5% is not a large increase. The fact remains it is difficult to begin to push beyond 85% and even more diificult to push beyond 90%. Although the difference is not large it does point out the fact that comparatively few inhibitors under such conditions show increased etfectiveness over a large number of available commercial inhibitors. Although thedifierence appears to be one of degree based on the percentage noted yet it is in fact a difierence in kind.

It should be pointed out that the corrosiveness of Well brines will vary from well to well, and the proportion of corrosion inhibiting agent added to the well fluids also should be varied from well to well. Thus, in some wells it may be possible to effectively control corrosion by the addition of-as little as 10 p.p.m. of the new compositions to the well fluids, whereas in other wells it may be necessary to add 200 p.p.m. or more.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent, is:

l. A method for inhibiting corrosion of ferrous metals by hydrocarbon fluids containing water and a member of the group of corrosive materials selected from the class consisting of hydrogen sulfide, carbon dioxide, organic acids containing 2 to 4 carbon atoms permolecule, combinations of these materials with each other, combinations of each of said corrosive materials with oxygen,

and combinations of said materials with each other and oxygen, comprising adding to said fluids at least 5 parts per million of the soluble basic reaction product obtained by heating at an elevated temperature up to about 280 C. a diamide of the formula in which R"CO is the naphthenyl radical of a naphthenic acid within the molecular weight range of 200 to 500 and in which the beta carbon atom is a part of a ring structure; R is an alkylene radical having not over 6 carbon atoms, R is a member of the class selected from hydrogen and low molal alkyl radicals having less than 8 carbon atoms, and n is a small whole number varying from one to four; said diamide derived product being obtained by a reaction involving polymerization by way of dehydration; said product being further characterized by the absence of a cyclic amidine structure and said dehydration of the diamide eliminating from .5 to 1.5 moles of water per molecule of diamide.

2. The method of claim 1 with the proviso that R is an ethylene radical and R is a hydrogen atom.

3. The method of claim 1 with the proviso that R is an ethylene radical, R is a hydrogen atom and RCO is the naphthenyl radical of a naphthen-ic acid within the molecular weight range of 275 to 350 and in which the beta carbon atom is a part of the ring structure.

4. A method for inhibiting corrosion of ferrous metals by hydrocarbon fluids containing water and a member of the group of corrosive materials selected from the class consisting of hydrogen sulfide, carbon dioxide, organic acids containing 2 to 4 carbon atoms per molecule, combinations of these materials with each other, combinations of each of said corrosive materials with oxygen, andcombinations of said materials with each other and oxygen, comprising adding to said fluids at least 5 parts per million of the soluble basic reaction product obtained by heating at an elevated temperature up to about 280 -C. a diamide of the formula H [H 1 NCgH4- NCiHa r-N ug (3R0 0 1) in which R"CO is the naphthenyl radical of a petroleum napli'thenic acid having an average molecular weight within the ranges 290-300, 320-330 and 410420 and having the average structure I H im. H imt H/ H and n is a small whole number varying from one to four; said diamide derived product being obtained by a reaction involving polymerization by way of dehydration; said product being further characterized by the absence of a cyclic amidine structure and said dehydration of the diamide eliminating from .5 to 1.5 moles of water per molecule of diamide.

5. The method of claim 4 with the proviso that n is l.

6. The method of claim 4 with the proviso that n is 2.

7. The method of claim 4 with the proviso that n is 3.

8. The method of claim 4 with the proviso that n is 4.

References Cited in the file of this patent UNITED STATES PATENTS 2,389,453 Perrine Nov. 20, 1945 2,468,163 Blair et al. Apr. 26, 1949 2,598,213 Blair May 27, 1952 2,677,705 Vtzinger May 4, 1954 2,756,211 Jones July 24, 1956 2,818,383 Jolly Dec. 31, 1957 

1. A METHOD FOR INHIBITING CORROSION OF FERROUS METALS BY HYDROCARBON FLUIDS CONTAINING WATER AND A MEMBER OF THE GROUP OF CORROSIVE MATERIALS SELECTED FROM THE CLASS CONSISTING OF HYDROGEN SULFIDE, CARBON DIOXIDE, ORGANIC ACIDS CONTAINING 2 TO 4 CARBON ATOMS PER MOLECULE, COMBINATIONS OF THESE MATERIALS WITH EACH OTHER, COMBINATIONS OF EACH OF SAID CORROSIVE MATERIALS WITH OXYGEN, AND COMBINATIONS OF SAID MATERIALS WITH EACH OTHER AND OXYGEN, COMPRISING ADDING TO SAID FLUIDS AT LEAST 5 PARTS PER MILLION OF THE SOLUBLE BASIC REACTION PRODUCT OBTAINED BY HEATING AT AN ELEVATED TEMPERATURE UP TO ABOUT 280* C. A DIAMIDE OF THE FORMULA 